208 DE. T. DAVIDSON ON EECENT BEACHIOPODA. 



Pi'ofessor Semper also published important observations on the animal of L'mcjula 

 nuathm in the ' Zeitschrift fiir wissenschaftliehe Zoologie,' Bd. xi. p. 100, 1862, and 

 in the " Ueisebericht " in the ' Zeitschrift fiir wissenschaftliehe Zoologie,' Bd. xiv. p. 424, 

 1864; and, lastly, Professor "W. King's instructive memoir "On some Characteristics of 

 Ziingula anatina," appeai'ed in the Ann. & Mag. Nat. Hist. 4th ser. vol. xii. 1873. To all 

 these works we shall again refer. The publications of Morse, Brooks, and others on the 

 animal of Glotlidia will also be alluded to under G. albida and G. Audeharti*. 



Having had the advantage of being able to study more than five hundred specimens of 

 Lingula anatinu, four hundred of which were collected by the ' Challenger ' Expedition 

 in a single locality, I observed that when quite young and up to 9 lines in length the 

 shell was completely elongated, oval and rounded at its anterior margin ; the beaks 

 tapei'ing more than in the adult condition. As the shell grows the sides become 

 subparallel and its front line nearly as wide as the rest of the shell, and slightly rounded 

 in front, with a small rounded mesial rib, which, commencing at about two thirds of the 

 length of the valve, forms at the front line a small projecting angle. The horny portion 

 of the shell, especially round its margins, is so thin that as the animal dries it bends over 

 or shrinks, sometimes to a considerable extent. The colour also varies very much in 

 different specimens, being generally of a more vivid or intense green at and close to the 

 concentric lines of growth Avhich cover its surface. In some places also the green is 

 more bright than in others on all the specimens. It is of a brilliant emerald-green in the 

 Philippine examples, but more sap-green in the Manilla specimens. The valves are not 

 exactly the same ; the ventral valve is somewhat the larger, and it has an acutely 

 tapering beak, with a channel along its middle, to which the long fleshy peduncle is 

 attached ; the beak of the dorsal valve is, on the contrary, obtusely rounded and shorter, 

 with a narrow, flattened, horizontally striated area on its inner surface. In the interior 

 of the valves an elongated lozenge-shaped area is occupied chiefly by the muscular and 

 other impressions ; here where the calcareous element prevails the shell is thickest, 

 the remaining portion of the valves being more essentially horny. 



The structure of the shell has been carefully investigated by Dr. Carpenter t, Di". Gra- 

 tiolet J, and M. S. Cloez §. Dr. Carpenter says: — "The structure of the shells of 

 Lingula and Orbiciila is peculiar. These shells are almost entirely composed of laminae 

 of horny matter, Avhich are perforated by minute tubuli, closely resembling those of 

 ivory in size and arrangement, and passing obliquely through the laminoe. Near the 

 margin of the shell, these tubuli may be seen lying nearly parallel to the surface." 



Dr. Gratiolet states that : — " There exists in the shell o? Lingula two distinct elements, 

 that is to say a horny element and a testaceous one j|. They are found arranged 



* [The more renoiit investigations of Dr. H. G. Beyer on the structure of Linrjula {Glottidia) i^nnmudata, Stimp- 

 son (' Studies from the Biological Lahoratorj- of Johns Hopkins University,' vol. iii. no. 5, March 1SS6), will bo 

 found summarized under Broderip's earlier described species Linr/tila (Glottidia) Audeharti, with which Dr. Davidson 

 found Liiir/ula pyramidata to be specifically identical. — A. C] 



t " On the Microscopic Structure of Shells," Eeport Brit. Assoc. 1844, p. 18. 



+ ' Journal de Conchyliologie,' 2« ser. vol. iv. 1800, p. 59. § Llnstitut, 1859, p. 240. 



II [Dr. H. G. Beyer records the presence of a third element in one genus of the Lingulida?, i. c. an outer •' cuticle," 

 differing in structure from the underlying so-called horny layers which alternate with the calcareous ones. See 

 anatomy of Glottidia Audeharti, p. 227. — A. C] 



